Author Topic: Example Project: 20 Channel solid state scan card for K2000 DMM (Read 26140 times)

voltsandjolts · « **on:** June 20, 2020, 06:50:36 pm »

I have previously posted a 10 channel armature scan card here:
https://www.eevblog.com/forum/circuit-studio/example-project-relay-scan-card-for-k2000-dmm/

I needed more channels for a particular job where a little SSR channel leakage wouldn't be a problem, here is the result.
It's been tested in K2000 and DMM6500.
It's switchable, 10 or 20 channels; some 2000 series gear might only support 10 channels (?), and saves some money if you only need 10 channels.
Initially I thought my K2000 would only support 10 channels but to my surprise the 20 channel card is supported too - at least it is in the latest firmware.

The PIC MCU firmware has a known issue when using with a DMM6500.
Switching between 2W and 4W resistance on the same channel causes the channel relay to open.
It works fine changing between channels in 2W and 4W.
I just need voltage measurements so didn't spend time fixing it, there's a note in the firmware source.

Thanks to forum members alm and cozdas for providing some background information and inspiration.

Edit:
I expect this card will NOT work in a K2001, K2002 or K2010 DMM for reasons described in this post.

FYI I adapted this card design to function in the Keysight 34970A/34972A DAQs, see here.

voltsandjolts · « **Reply #1 on:** June 20, 2020, 06:51:32 pm »

CircuitStudio Project attached in 7-Zip format

jaudo · « **Reply #2 on:** September 24, 2020, 10:57:45 pm »

Looks amazing!

I'm starting with Circuit Studio. I've seen you are manufacturing with JLPCB. Could you export the .rul file for us (if it's designed for JLPCB manufacturing?) this would save me a lot of time.

voltsandjolts · « **Reply #3 on:** September 25, 2020, 05:38:00 pm »

I was quite lazy about rules in that project, probably better to use this:
https://github.com/ayberkozgur/jlcpcb-design-rules-stackups

Yansi · « **Reply #4 on:** September 25, 2020, 05:43:45 pm »

The "spare SSR" area on the board is funny.

Also quite surprised about the claimed <1nA typical leakage of the SSR in off state. (but still it doesn't beat a proper reed relay)

voltsandjolts · « **Reply #5 on:** September 25, 2020, 06:03:18 pm »

Quote from: Yansi on September 25, 2020, 05:43:45 pm

The "spare SSR" area on the board is funny.

Hah, yeh, lots of board area going to waste so why not!
I'm quite experienced in letting the smoke out of SSRs

mtnzap73 · « **Reply #6 on:** October 10, 2020, 02:52:09 am »

The DMM6500 datasheet on page 12 has the following:

Temperature Characteristics
.....
Thermocouple Reference Junction External (CJC on 2001-TCSCAN or user-provided with 2000-SCAN) or simulated (fixed)
......

The 'user-provided with 2000-SCAN': does this mean that a user can connect a Thermocouple Reference Junction to a 2000-SCAN card? (like the 2001-TCSCAN card which comes with the reference)

Most if not all temperature measurement info leads to the 2001-TCSCAN card.

voltsandjolts · « **Reply #7 on:** October 10, 2020, 11:43:17 am »

You could make a reference junction but its probably simpler to use a PRT and 4W resistance measurement.
The Ohms to degc calculation is shown in this post:
https://www.eevblog.com/forum/circuit-studio/example-project-relay-scan-card-for-k2000-dmm/msg2884320/#msg2884320

Anders Petersson · « **Reply #8 on:** January 31, 2021, 01:54:20 pm »

Many thanks, I'd be happy to get away from the clicking of 2000-SCAN, but I wonder about the downsides of using solid-state relays?
The specified Vishay VOR1142M4 (http://www.farnell.com/datasheets/2614513.pdf) lists typical on-resistance as 22 ohm.

And at least DMM6500 lists max 4-wire ohms lead resistance as

Quote

5 Ω per lead for 1 Ω range
10% of range per lead for 10 Ω, 100 Ω, 1 kΩ, and 10 kΩ ranges
1 kΩ per lead for 100 kΩ, 1 MΩ, 10 MΩ, and 100 MΩ ranges

Does this mean this scan card is only suitable to measure 1 kΩ and higher?

voltsandjolts · « **Reply #9 on:** February 04, 2021, 01:01:37 pm »

Yes, you're correct.

SSR selection is a compromise between leakage current and on-state resistance. Since the more common scenario is scanning for voltage measurements, where on-state resistance doesn't matter much, I chose the VOR1142 for its primarily for its low off-state leakage current. It also has good contact voltage rating and isolation rating.

You could look around for other SSRs in same package, with a lower on-resistance which would suit your use case better.

Anders Petersson · « **Reply #10 on:** February 11, 2021, 03:22:58 pm »

I looked around and found Omron G3VM-61VY2 (https://omronfs.omron.com/en_US/ecb/products/pdf/en-g3vm_61g_61vy1.pdf)
On-state resistance typ. 1 ohm, max 2 ohm
Off-state leakage typ. 0.1 nA, max 1 uA
The only downside I see is the rating for 60 V, where VOR1142M4 has 400 V.

And depending on how lucky one feels, the worst-case G3VM-61VY2 leakage of 1 uA is higher than VOR1142M4 0.1 uA (at up to 100V).
Wonder why Omron specifies a worst-case leakage 10000x higher than the typical leakage.

voltsandjolts · « **Reply #11 on:** February 11, 2021, 08:50:23 pm »

For 60V max applications that Omron looks like a fair choice.
It's a little slow at 2ms max turn-on but I doubt the keithley firmware will be scanning anywhere near that fast even at low resolutions.
For manufacturing, the wide typ/max range helps with semiconductor yield (less failures) and 1uA makes device test faster/easier = cheaper.
Most will be way closer to typical than max.
Of course, you could do your own selection testing to pick the best of a batch if critical.

Anders Petersson · « **Reply #12 on:** February 11, 2021, 10:04:43 pm »

Thanks!
A faster variant, but a bit higher resistance and leakage, is https://www.vishay.com/docs/84724/vo1400aeftr.pdf
leakage typ. 2 nA (max 1 uA)
On-state resistance typ 2.3 ohm, max 5 ohm
Turn-on max 500 us
Rated 60 V

With these two options, I'm confident to try it out.

By the way, the closest commercial equivalency I find is Keithley 7710 (http://www.farnell.com/datasheets/1884807.pdf) that states "Actuation time <0.5ms" and "Scanning speeds of up to 500 channels/second". Also, it's 60 VDC and 5 ohm.
...and about 10x the price of DIY.

KedasProbe · « **Reply #13 on:** February 25, 2021, 09:19:18 am »

What is the cost of the PCB?
Anyone in Europe with some PCB order experience wants to order a few more empty PCB's and sell it?
(this will reduce the fixed cost much)

edit:
I tried https://cart.jlcpcb.com/quote with the provided zip file.
It's like 20 euro for 10 plus shipping, is it that cheap or am I missing something here?
4 SSR components will cost me more than 1 PCB.
And they have the vo1400aeftr in their library if you want them to assemble, probably also cheaper than buying it separately. (only one side can be done though, maybe they should al be moved to the top side.)

KedasProbe · « **Reply #14 on:** February 26, 2021, 04:42:58 pm »

Is there is 3D enclosure model for 3D printing or is it not really required to hold it in place in a DMM6500?

voltsandjolts · « **Reply #15 on:** February 26, 2021, 05:50:02 pm »

No enclosure required, it fits as-is.
Some (all?) of the OEM modules have covers to reduce risk of electric shock.

KedasProbe · « **Reply #16 on:** February 27, 2021, 01:03:45 pm »

This may also be good alternative for the VO1400AEF
https://jlcpcb.com/parts/componentSearch?searchTxt=CPC1014N
Is more expensive but can handle more current with a bit lower resistance and has a low typical leakage.

I installed the trial of CircuitStudio, is there a way to export this project to a free software package?

voltsandjolts · « **Reply #17 on:** February 27, 2021, 02:11:22 pm »

I think this importer is a work-in-progress but might be of some help, never tried it.
https://forum.kicad.info/t/work-in-progress-native-altium-importer/20712

KedasProbe · « **Reply #18 on:** February 27, 2021, 04:16:30 pm »

Tried to see what it would cost with their (jlcpcb) free assembly coupon but they don't have any component in stock (even if it's in their database)
So I will just order 5 PCB's without any modifications.

Their Analysis gives:
layers : 2
minimum trace width : >=10 mil
minimum trace spacing : >=10 mil
minimum drill size : 0.406 mm
width : 228.6 mm
height : 71.89 mm

So I guess the provided zip file is ok for them.

edit: for 5 PCBs (I could order 10 but then they will just not be used)
Merchandise Total: €9.34
Shipping Charge: €15.81
Order Total: €25.15 (including taxes)

KedasProbe · « **Reply #19 on:** February 28, 2021, 02:25:01 pm »

Some comparison, since I have at least 2 weeks to choose components

I may order 2 or 3 to measure them.

KedasProbe · « **Reply #20 on:** February 28, 2021, 05:32:50 pm »

Since I haven't setup a scanner card before, how is the delay between 'change channel' and the measurement on that channel arranged?
Is that a set delay by the user or a fixed value of the device?

Edit:
Since nobody is reacting I assume the devices are usually slower than the SSR relays to start a measurement hence no delay actions required, 'how slow' is something that will need to be tested I guess.

I'm planning to make an 10 channel with VOR1142M4 and an 10 channel with G3VM-61VY3
(why not 20, well I don't see myself using it yet so I can always upgrade later)

KedasProbe · « **Reply #21 on:** March 10, 2021, 10:23:58 am »

I received the PCBs from JLCPCB today, for those interested, pictures attached.
The only changes I did from default was lead free and blue instead of green.

KedasProbe · « **Reply #22 on:** March 22, 2021, 08:25:37 am »

Since I didn't noticed the link mentioned here, this is another project based on the work already done by others.
This one is with an STM32
https://www.christidis.info/index.php/personal-projects/keithley-dmm-scanner-card-with-ssr

czecht · « **Reply #23 on:** May 01, 2021, 03:39:59 am »

I would like to buy couple of the PCB's from you and also, if you have all the parts for it, just let me know what you need from me and the price. I live in Lincoln, Nebraska, USA 68505 and my personal email is czecht@gmail.com
Do you have youtube channel?
Or some other place to see your videos?
Did you make a video how to assemble the PCB?
Is it working now?
My Keithley is DMM6500 and I just purchased it few days ago.
Thank you very much.
Tony

KedasProbe · « **Reply #24 on:** May 05, 2021, 06:39:29 pm »

This is what I ordered but I haven't assembled it yet it's an "important but not urgent" project so I don't know yet if I'm missing something or not.
To order the PCBs it's 25 euro for 5 so there isn't really much profit in shipping spare PCBs around.
For components it's about 70 euro for one 10 channels card. (this BOM is for 2 different cards)

It also includes a pickit programmer since I didn't have one so you may want to remove that, and maybe buy a few less spares.
The STM32 version above is maybe a better option.


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Author Topic: Example Project: 20 Channel solid state scan card for K2000 DMM (Read 26140 times)

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